1. Field of the Invention
The present invention relates to a semiconductor process, more specifically, to a method for forming a deep trench capacitor of a semiconductor memory.
2. Description of the Prior Art
Deep trench capacitors have been widely employed in the conventional semiconductor memory (such as DRAM) process, in order to reduce the occupied areas and to increase capacitances. FIGS. 1a and 1b present parts of a conventional deep trench capacitor process. The deep trench structure in FIG. 1a comprises a substrate 11 usually being a silicon substrate, a pad oxide layer 12, a pad nitride layer 13 usually being SiN, a trench 14, a buried plate (BP) 15 (i.e., the bottom electrode), a dielectric layer 16 usually containing nitride and oxide, a conductive layer 17 used as an upper electrode and usually being polysilicon, and an insulation layer 18, which is oxide usually and is used to form a collar oxide layer in the trench 14 in the subsequent process. Later, in FIG. 1b, the insulation layer 18 on the pad nitride layer 13 and the conductive layer 17 is removed by dry etching, for example, and the trench 14 is filled with the conductive layer 19, which is used as a connection electrode, by deposition and etching, for example, to engage the conductive layer 17. Then, a buried strap (BS) (not shown) is formed on the conductive layer 19 to engage an adjacent transistor (not shown), which is subsequently formed.
However, as shown in FIG. 1c, the aforementioned process would generates a conductive layer 17′ with a recess and thereby generate an insulation layer 18′ with a recess. Later in FIG. 1d, part of the insulation layer 18′ remains in the recess of the conductive layer 17′ after the removing of the insulation layer 18′ on the pad nitride layer 13 and the conductive layer 17′, and creates poor electrical connection between the conductive layer 19′, which is subsequently formed, and the conductive layer 17′, while the conductive layer 19′ comprises a recess as well. In an extreme situation, the residual insulation layer 18′ left in the recess still connects with the insulation layer 18′ on the sides of the trench, so that the electrical connection cannot be formed by the conductive layer 19′ and the conductive layer 17′ and the deep trench capacitor is ineffective.
Therefore, a need for overcoming the above problem is required. The present invention fulfils this need.